The present invention relates to oil production and in particular to a sucker rod guide centralizer for preventing production pipe and sucker rod wear by reducing friction forces between them.
Oil is withdrawn from subterranean formations through a tubular production pipe formed from a string of tubing extending to the surface. The oil is lifted through the pipe by the action of a downhole pump actuated by a sucker rod string which is reciprocated at the surface by a pump jack. A sucker rod string is made up of a multiplicity of individual sucker rods joined together end to end. Each sucker rod comprises a main stem having a diameter typically in the range of from 3/4" to 11/2" and a length of about 30 feet.
In recent years, directional and deviated wells have become very popular in many oil fields. The use of sucker rod strings in directional or deviated well bores has had problems. The rod string usually formed from steel tends to lie along the low side of the production pipe and with time reciprocation of the rod string tends to wear away the wall of the pipe. Additional problems arise from the steam injection techniques used to improve the production of heavy and extra heavy crude oils.
Attempts have been made to deal with the frictional problems associated with tools or tubular structures used in production pipes by incorporating a centralizing device therein which serves to space the tool or tubular structure from the production pipe tubing and thereby reduce wear of the tubing wall. These centralizing devices have taken different forms such as a series of projections on the outer periphery of a coupling member and rollers or bearings incorporated within the structure of the sucker rod. U.S. Pat. No. 2,722,462 to Tschirley illustrates one such device comprising an elastomeric collar having a row of bumps or projections attached to a drill pipe. The bumps on the collar are designed to maintain a desired separation between the pipe and the surrounding casing. U.S. Pat. No. 3,938,853 to Jurgens et al. illustrates a similar stabilizing device secured to a drill collar. The device has an inner sleeve and an outer sleeve with a series of longitudinally extending helical ribs. The primary deficiency of these devices is believed to be their tendency to wear out as a result of the frictional contact between the fixed centralizing elements and the production pipe.
U.S. Pat. Nos. 2,466,239 to Holcombe, 2,601,748 to Weir and 4,577,327 to Kinley et al. illustrate guides using rollers or bearings. In Holcombe, a series of wheels or rollers are mounted to a rod by a wing and keeper plate arrangement. In Weir, the bearing balls used to guide the sucker rod are located in a series of longitudinally extending grooves having intermediate races about the periphery of the rod. In Kinley et al., the centralizing device comprises a plurality of spring loaded centering arms having a series of rollers in a center segment.
More recently, a centralizing device comprising a coupling device having a cylindrical body and a plurality of lenticular wheels positioned within slots in the body has been developed. To minimize scoring of the tubing wall, the wheel members are formed of a hard, non-abrasive material such as hard nylon. U.S. Pat. No. 4,621,690 to Klyne illustrates such a device.
Many of these devices when tested in wells having a temperature above 500.degree. F. have failed in giving high performance work life. Often, the non-metallic components of the devices are the weak links because they cannot withstand the critical conditions in the oil wells. In the wheeled devices, failure is also often the result of too few wheels being in contact with the production pipe tubing.
Accordingly, it is an object of the present invention to provide a device for centralizing a sucker rod string within a production pipe and for reducing frictional forces therebetween.
It is a further object of the present invention to provide a device as above capable of withstanding typical oil well service conditions.
These and other objects and advantages will become more apparent from the following description and drawings.